Fix(ui): an empty MAC Lookup submit clears the last answer

Returning early on empty input left the previous result and error on
screen. It now clears them first, and the button stays disabled for a
whitespace-only input.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/components/advanced-tools/MacChecker.vue

@@ -18,7 +18,7 @@
                     :placeholder="t('macchecker.Placeholder')"
                     v-model="queryMAC" @keyup.enter="onSubmit" :aria-invalid="errorMsg !== ''" />
                 <Button variant="action"
-                    :disabled="macCheckStatus === 'running' || !queryMAC"
+                    :disabled="macCheckStatus === 'running' || !queryMAC.trim()"
                     @click="onSubmit" class="cursor-pointer">
                     <Spinner v-if="macCheckStatus === 'running'" />
                     <template v-else>
@@ -178,11 +178,12 @@ const validateInput = (input) => {
 };
 
 const onSubmit = () => {
-    const raw = queryMAC.value.trim();
-    if (!raw) return;
-    trackEvent('Section', 'StartClick', 'MACChecker');
     errorMsg.value = '';
     macCheckResult.value = {};
+    const raw = queryMAC.value.trim();
+    // Empty input (Enter in a cleared field) just clears the last answer.
+    if (!raw) return;
+    trackEvent('Section', 'StartClick', 'MACChecker');
     picked.value = EXAMPLES.some((e) => e.input === raw) ? raw : '';
     const query = validateInput(raw);
     if (query) getMacInfo(query);